Revert "dmaengine: pxa_dma: add support for legacy transition"

This reverts commit c91134d9.

The conversion of the pxa architecture is now finished for all
drivers, so this functions has fullfilled its purpose and can
now be removed.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>